Kauaʻi or Kauai (; Hawaiian: ) is geologically the oldest of the main Hawaiian Islands. With an area of , it is the fourth largest of the main islands in the Hawaiian archipelago, and the 21st largest island in the United States. Known also as the "Garden Isle", Kauai lies across the Kauai Channel, northwest of Oahu. This island is the site of Waimea Canyon State Park.